Thermal Non-equilibrium Plasma Observed by Hinode

Abstract

Plasma in the solar corona is believed to be in thermal equilibrium because of the occurrence of weak Coulomb collisions. To date, many studies have discussed the plasma dynamics in the solar corona assuming thermal equilibrium. Most phenomena observed in the solar corona can be explained under this assumption because the available temporal resolution is not sufficient to resolve non-equilibrium conditions. After Hinode was launched, a very high temporal resolution became available, especially for spectroscopic observation. Now, we can discuss plasma heating or acceleration in the solar corona using extreme-ultraviolet spectroscopic observations with high time resolution. Further, we can also observe the solar corona at multiple wavelengths with high spectral resolution. Owing to Hinode observations, we can now discuss plasma dynamics under thermal non-equilibrium conditions, such as non-equilibrium ionization. Recently, thermal non-equilibrium plasma has received attention not only in the field of solar physics but also in other fields such as X-ray astronomy.